Remote manipulators are used in a wide variety of applications. One of the most demanding applications for remote graspers is in surgery. The use of remote manipulators in surgery is becoming increasingly important. For example, various surgical operations can now be performed laparoscopic,ally through the use of appropriate laparoscopic graspers. These surgical procedures would be impossible without elongated graspers which can act as extensions of the surgeon's hand for remote manipulations at locations inside a patient's body.
A laparoscopic grasper typically comprises a lever which can be moved by a surgeon. The lever is typically mounted adjacent to a fixed handle so that the surgeon can control the lever with one hand by squeezing the lever toward the handle. The lever is connected to the jaws of a grasper by a mechanical linkage. Typically the linkage comprises a number of links which are connected to provide a ratio of lever movement to grasper movement (or "transmission ratio") which is less than 1:1.
One problem with such graspers is that they do not provide the surgeon with very good force feedback. The surgeon often cannot tell how tightly the grasper is gripping an object because the transmission ratio of the linkage is not 1:1. Furthermore, friction is inherent in the mechanical linkage. Free play which generally occurs in the joints of any mechanical linkage also deleteriously affects the force feedback to a surgeon. These problems are compounded because the ratio of the force being applied to the handle by the surgeon to the force being applied to the grasper tends to vary significantly with the mechanical properties of the object being grasped as well as with the degree of opening of the grasper. As a result, of these factors, surgeons have less control over the forces exerted by remote graspers than is desirable. There have been a number of injuries to patients undergoing laparoscopic surgical procedures. Some of these injuries can be attributed, at least in part, to the lack of accurate force feedback in currently used laparoscopic graspers.
Various attempts have been made to design mechanical remote graspers which have low friction losses and have force transmission functions which are nearly constant. Such designs yield improvements in some areas. These designs are still not optimal because they do not allow the force transmission function to be easily adjusted. Preferably the force transmission function can be adjusted so that the forces exerted at the handle to yield a desired range of forces at the grasper lie in the range where the surgeon's hand has the greatest force sensitivity. Another problem with such mechanical graspers is that they provide no mechanism for limiting the maximum force that can be applied by a grasper.
Others have provided systems for operating a remote grasper completely under computed closed loop feedback control. Such systems are often very complex and suffer from the additional disadvantage that the systems fail completely if their computer controllers malfunction. Further, such systems often use bulky and/or very expensive actuators to drive the motion of the grasper. Two examples of such systems are U.S. Pat. Nos. 5,623,582 Rosenberg and 5,625,576 Massie et al.
Remote manipulators have many applications other than surgery. For example, remote manipulators may be used to manipulate hazardous materials or to service parts of machinery which cannot be reached with a human hand. Many of these applications also require a remote manipulator which provides force feedback to a user, adjustable force transmission function and a mechanism for preventing excessive forces from being applied to the output portion of the remote manipulator.
There is a continuing need for a remote grasper in which the maximum amount of output force can be limited. There is also a continuing need for remote manipulators which provide adjustable force transmission functions. There is a particular need for such remote manipulators which are compact, light in weight, and simple in construction.